Fauna of Anemonefishes (Pomacentridae, Amphiprioninae) and Their Host Sea Anemones (Cnidaria, Actiniaria) of the Hon Rom Coral Reefs (Southern Central Vietnam, Nha Trang Bay) and its Changes for the Period from 2003 to 2018

The fauna of the anemonefishes (Pomacentridae, Amphiprioninae) and their host sea anemones , inhabiting the detached coral reef of the Hon Rom Island, has been first described. Changes in faunas of these groups over 2003–2018 were traced. The species (qualitative) composition of these groups did not change over the period indicated above. It includes four anemonefish species: Amphiprion clarkii , A. frenatus, A. perideraion , and A. sandaracinos and six sea anemone species symbiotic with them: Entacmaea quadricolor , Stichodactyla mertensii , Heteractis aurora , H. crispa , H. magnifica , and H. malu . Four of these host sea anemone species ( S. mertensii , H. magnifica , E. quadricolor , and H. crispa ) belong to the principal host sea anemones of the reef anemonefishes, i.e. ensure the long-term existence of spawning pairs of symbiont fishes . However, quantitative changes in the faunas of the study groups have occurred. Two host sea anemone species ( S. mertensii and H. magnifica ) and mature anemonefishes inhabiting them were recorded each year in the observation period. The number of the sea anemones S. mertensii reduced by two thirds to 2018, compared to that in 2003–2005, and 100% of adult A. sandaracinos disappeared, while the number of adult A. clarkii within the study sea anemone species reduced by one third. The number of sea anemones H. magnifica reduced by 20% until 2018, compared to that in 2003–2010; 40% of adult A. perideraion disappeared. At least a threefold decrease in the pairs number of the anemonefish A. frenatus within the sea anemones E. quadricolor was observed; pairs of the anemonefish A. clarkii replaced them. It has been shown that there is no displacement of spawning pairs of A. sandaracinos , A. perideraion , and A. frenatus , respectively, from their host sea anemones S. mertensii , H. magnifica , and E. quadricolor , but there is replacement of these anemonefish species in the fish-free sea anemones by another anemonefish species— A. clarkii .